Ife Journal of Agricul~ure,Vol. 12, Nos. I & 2 1990 Dormancy and Germination of

GODWIN J. ESENOWO Department of Botany Obafemi A wolowo University Ile-Ife.

Abstract The of Mucuna urens (L) have two sizes designated as small (SS) and large (LS) which occur in the ratio of 3: 1. Both sizes of seeds are dormant. These dormant seeds were successfully germinated after various methods had been used to terminate the coat dormancy. The most successful method was scarification with concentrated HZS04 for one hour, which gave 90% germination. Heat treatment and seed coat removal also helped to break the dormancy of these seeds. It was observ- ed that at 83OC days to germination in M. urens increased with time while percentage germination decreased with time.

Iotroduction

Mucuna ,urens, . a lso known as Horse Eye , occurs in Nigeria, Ghana and Sierra Leone. -.I ms piant. is a climber and it fruits between July and August. The fruit is covered with stinging hairs. The seeds are flat, reddish brown in colour, and about 3-8 cm in diameter. The hilium is about 4/5 of the circumference (Irvine, 1962). The stem and leaves of the Mucuna , in combination with the fruit of - Alihornea cordifolia yield a black or blue dye. The stem and flower stalk are used as rough fibre. Mucuna urens is also used as beverage and has medicinal value (Irvine, 1962). In Nigeria, the seed is very important to southerners because it is used in thickening soup and also used in games. Although this crop seems to be preserved by those that know its value, some factors have contributed to its low population densi- ty in the field. One of this is bush clearing and uncontrolled bush burning which are rampant-in the dry season. Bush burning destroys the seedling and reduces the population density. One other factor is excessive grazing by livestock. These animals also destroy the seedling physically by their trampling through the field. Another factor is the formation of surface moulds when the seeds are planted. These moulds pel eadily in to the embryo a nd affect seed viability (Kozlowski, 1972). Pel nore important fa ctor is th le fact that only a few seeds germinate in the .-a:-- 11I--* -P *L fieb a1 rcr lllally 111u1iths--- af plit11~111~.IVIUSL UI LIZ seeds are dormant. There is no information on studies of germination and dormancy of Mucuna urens. Hence, this paper describes the different ways of breaking the dormancy and - germination of M. urens. Mattriala and Methods

Seeds used in this study was collected.from 12 randomly selected trees in the field during fruiting period in Uyo, Akwa Ibom State. Collections were made and obser- vation revealed that two types of seeds were present in the lot. The seeds were separated into two sizes designated large seeds (LS) and small seeds (SS). This ex- periment was carried out in the Department of Botany, Obafemi Awolowo Universi- ty, Ile-lfe.

Germination Studies

Two batches of 100 large seeds and 100 small seeds were selected and soaked over- night in sterile distilled water. The seeds were planted in plastic buckets (16 x 20 cm) - containing sterilized soil and were placed in the screen house. The seeds were = watered as need arose. The buckets were in ten replicates and were incubated at 27 k 1OC for 40 days. The emergence of the seedlings from the soil was used as the basis of determining germination of seeds. A second batch of large and small seeds was planted as earlier described and in- cubated at various temperatures ranges of 10°C, lS°C, 25"C, 30°C, '35°C and 40°C. Ten replicates were also I

Dormancy Studies

Heat Treatment

These dormant seeds were subjected to heat treatment in order to break dorman- cy. Ten seeds were placed in a water bath at each of the specified temperatures 100"C, 90°C, 83"C, 70°C, 60°C and 50°C and the following time exposures: 1,2,5, 10, 15 and 20 minutes were used for each temperature tested. Heat treatment was - carried out by immersing the seeds in water at the specified temperature. Seeds were planted as earlier described. Percentage and days to germination were recorded for different temperature and time combinatiorl treated (Tables 4 and 3).

Seed decoating

Partial testa removal of M. urens seeds was done by removing the seed coat from either the macr opyle or nonmicr ophyle end of the seeds. This was performed by using a sterile k:nife and forceps. Total decoating involved the removal of the seed coat. 100 seeds were us1 ed for estch treatment. The decoated seeds were surfaced sterilized with 0.1 % me doride solution for 30 seconds and washed with several changes of distilled water before planting in large sterile petri dishes. Each petri dish contained fo~Ir sterile filter papers soakcd with sterile distilled water. These dishes were incubareaA-J at-A 3uoC-#,< for 40 days.

Acid scafification * These seeds were scarified by immersing in different types of concentrated acids for various periods. Concentrated acids used were HNO3, H2S04, HCI for 1,2,5, 10, 15, 30 and 60 min. res~ectively.Acid was vlaced in the beaker just enough to - cover 1the seeds,.Seeds! were soak:ed in ru~ming -tapI water fc~r 3 hours after the acid had bc !en poure d off. T1re treated seeds wc :re plantcd in buclcet with sterilized soil as above and imc arified se eds were planted aIS control The effd of herbicide andfungicide on the seeds

Fiver herbicide and one fungicide (Table 5) were tested on the dormancy of Mucum urens seeds. These seeds were exposed to the concentrated commercially formulated herbicides and fungicide as was described for acid scarification. The seeds were then planted in sterilized soil as earlier described.

The effect of growth regulators on the dormancy of M. urens

Different growth regulators were also tested on the dormancy of the M. urens seeds. Ten seeds were presoaked for 3 days in a solution of ethrel, thiourea, gib- berellic acid (GA3), indole acetic acid (IAA) and kinetin at the concentration of 0, 10, 100, 200 ppm respectively and then planted in buckets with sterilized soil. Con- trol seeds were soaked only in sterile distilled water for 3 days. Ten replicates were also used. Records of germination were taken 40 days after planting.

The ratio of the large seeds (LS) to the small seeds (SS) was found to be approx- imately 1:3 (Table 1) Germination studies indicate that both small and large se~dsof M. wens did not germinate after 40 days, at various temperature treatments (Table 2). Both were dormant. 30% germination was obtained at 83°C for 10 min. and - 20% at 83°C for 15 min. 20% germhation was obtained at 70°C for 15 min (Table 4). At 83°C days KO germination of M. urens. increased with time (Table 3). Untreated seeds did not germinate (the control). I Partial or total testa removal from dormant seeds showed increased germination over the heat treatment (Table 4). Partially decoated seeds at the micropyle end had 70% germination, seeds decoatcd at the non-micro~vleend had 60% germination. totally decoated seeds had 80%. while scarification with concentrated sulphuric acid gave 90% germination in 60 min. Soaking of these dormant seeds in herbicide, fungicide, and growth regulators did not induce their germination (Table 6).

TABLE I: The ratio of distribution of I2 sampks of M. unmcollecled from the field.

Total Ratio of SmaNscdr Iarge srdr coNected SS:LS

90 (89.5) + + 30 (30.5) 120 3:l a0 (59.7) 20 (20.3 j 80 3:1 80 (74.6) 20 (25.4) 100 4:1 54 (53.8) 18 (18.2) 72 3: 1 30 (33.6) I5 (11.4) 45 2:1 150 (149.1) 50 (50.9) 200 3:l 1401156.6) 70 (54.4) 210 2:1 165 (164.2) 55 (55.8) 220 3:l 192 (179.0) 48 (61.0) 240 4:l 220 (223.7) 100 (76.2) 312 2: 1 234 (232.7) 78 (79.3) 312 3:1 320 (298.4) 80 (101.6) 400 4:l

,1715 I 584 2299 3: 1

+ +Large vs small sizes were rignifiilly different at P (0.05.

I% figures in brackets arc expected values. TABLE 2: Percentage germination of M. urens under various temperature for 40 days. Data averages of 10 replicates

Percentage germination

Seed type 10°C 15°C 25°C 30" 35°C 40°C

Large seeds 0 0 0 0 0 0 Small seeds 0 0 0 0 0 0

TABLE 3: Days of germination of M. urens at various temperature+ and time + +

Temperature in Time in minutes Total "C I 2 5 f 10 15 1 20 1-

Control (25 "C) 0 0 0 0 0 0 0 50 0 0 0 0 0 0 0 60 0 0 0 0 0 0 0 70 0 0 0 0 24 0 24 83 0 0 0 19 18 2 1 58 90 0 0 0 0 0 0 0 100 0 0 0 0 0 0 0

Total 0 0 0 19 42 2 1 82

+ + Not significant at P 0.05 (tweway ANOVA) + Significant at P < 0.05 (two-way ANOVA)

TABLE 4: Effect of different treatments on the percentage germinatioa of M. urens

Different treatments + + PartbIfy Partia I fy Total H2S04 acid decmted decmted decoated seeds seeds at see& scan'flcation at micropyle non-micropyle for 60 min. end end

70 60 90 100 65 50 70 90 75 70 80 80 Total 210 180 240 270 Mean 70 60 80 907

+ +Significant at P <0.01 {one wav ANOVA)

82 TABLE 5: Percentage germination of M. urens at various temperature+ and time + +

Temperature m , Time in minutes Total 1 20 "C 2 5 10 15 , Control (25 "C) 0 0 0 0 0 0 0 50 0 0 0 0 0 0 0 60 0 0 0 0 0 0 0 70 0 0 0 0 20 0 20 83 0 0 0 30 20 10 60 90 0 0 0 0 0 8 0 100 0 0 0 0 0 0 0

Total 0 0 0 30 40 10 80

TABLE 6: Percentage germination of M. u~mafter soaking with various chemicals. Data arc averages of 10 replicates.

&mure time (minuted Chemicak I 5 10 15 1 30 40 60 Control 0 0 0 b 0 0 0 HCl 0 0 0 0 0 0 0 0 H2m4 0 0 0 0 0 0 0 90 HNo3 0,o 0 0 0 0 0 50 Atrazine 0 0 0 0 0 0 0 0 2.4 D 0 0 0 0 0 0 0 0 EPTC 0 0 0 0 0 0 0 Molinatc 0 0 0 0 0 0 .O

Monuron 0 v 0 0 0 0 0 0 Gammalin 20 0 0 0 0 0 0 0 0

+ Not significant at P > 0.05 (Two-way ANOVA) + + Significant at P C;0.05 (Two-way ANOVA) c Discussion

The ratio of occurrence of small size to large size seeds was approximately 1:3 and were significantly different at (P 4 0.05). The occurrence of these sizes of seeds could be attributed to genetic influence (Etejere et al., 1982). In this study seed decoating gave increased germination over heat treatment. This result is in line with the study of Etejere et al. (1982) who found that partial or total decoating of dark . brown Parkia chapertoniana seeds showed improved germination over the heat treatment. - M. urens is a leguminous plant that is characterized by hard seed coat and long lived seeds which are mechanically resistant and impermeable to water (Fordham, 1%5). It is likely that the dormancy of M. urens is due to seed coat impermeability. Similar seed coat impermeability has been reported in Parkia auriculata by Coutinho and Stmffaldi (1971). Usually, dry seeds have a low moisture content and will not absorb water until the seed coat is penetrated by abrasion, preheating or microbial action (Gerumond, 1978). The hard seed coat and low moisture content permit a long period of dorman- cy and viability mores and Mora, 1984). In dry seeds, it is often the case that the higher the temperature, the shorter the dormancy period, as in most cereals and grasses. Because of this relationship, it is often possible to treat any seed with relatively high temperature for a few days to remove dormancy (Roberts, 1965). Similar observations were shown in the M. urens germination. In this study, it was observed that the germination days of M. umm increased with increased period of heating while high heat increased the percentage germina- - tion of M. urens. The high heat treatment breaks the dormancy of Mucuna umns. by making the seed permeable to water Kozlowski (1972). It might also hve lowered the wncentration of certain growth inhibitors accumulating in the seeds during their development. Etejere et al(1982) obtained the highest germination of Parkia claper- toniana with acid scarification but germination was inhibited by fungidde and her- bicide. In the germination of M. urens scarification with concentrated sulphuric acid for 60 min. gave 90% germination while herbicide and fungicide did not break the dormancy of these seeds. Auxin and gibberellic acid seed treatment have been shown to remove dormancy and accelerated germination (Kozlowski, 1972). In contrast, growth regulators did not break the dormancy of these seeds. The percentage germination of M. urem is low in the field as compared with other . This is further evidenced by the nwber of dormant seeds and their poor response to different treatments. In the field, the condition is worse when the hard seed coats are softened only by alter- nating temperature and biological activity of the soil flora and fauna. It may take several weeks or even months for the seed coats to be degraded by biological activity for germination to proceed smoothly. With increased percentage germination of dormant M. urrnr with heating and scarification treatment, there seems to be a ray of tope of increasing the population of this amnomic crop in the field. Aramide, S.A. 1976. Seed dormancy and germination in some rnoraceous plants. M. Sc. Thesis, University of Ibadan. a Coutinho, L.M.L. and Struffaldi, Y. 1971. Observations on seed germination and seedling of leguminous plants of Amazon forest gaps. Parkia auriculata Phyton Dev. Int. Bot. Erpt. 28: r Etejere, E.O. Fawole, M.O. Sani, A. 1982. Studies on the germination of Parkia clapertonia~Turrialba 32: 181-185. mores, E.M. Mora, B. 1984. Germination and seadling growth of Pithocellobiurn arboreurn Urban. Turrialba 34: 485488. Fordham, A. J. 1965. Germination of woody legume seeds with impermeable seed coat. Arnoldia 25: 1-8. Gerumond, H. 1978. Physiological aspect of seed germination. Seed Science and Technology 6: 625-639. Irvinc, F.R. 1962. The woody plants of Ghana. 2 edn. Oxford University Press, 397. Koilowski, T.T. ed. 1972. Seed Biology. AccrdernicPress Inc. New York. Roberts, E.H. 1%5. Dormancy in Rice seed. IV Varietal responses to storage and germination temperature. J. mt.Botany. 16: 341394.